[Synthesis of oligodeoxyribothymidylate derivatives containing alkylating groups and residues of biotin, for directed modification of chromatin].

: An oligodeoxythymidylate derivative bearing an alkylating group at the 5'-end and biotin at the 3'-end (RCl-(pdT)16-bio) was synthesized. This reagent alkylates polyA-tracts of DNA in HeLa nuclei specifically via complementary complexes with single-stranded segments of DNA and by the preliminary treatment of chromatin with S1-nuclease, since the reaction is inhibited by an excess of the corresponding free oligothymidylate. The reagent will be used to study the distribution of local unwinded parts of polyA-repeats of DNA in human chromatin by the electron microscopy.